Friday, August 27, 2010

Sunspots Squeeze and Stretch the Day

Most of us don't notice it, but not all days are the same length. Now it seems that sunspots -- dark regions that emerge on the sun's surface -- may be partly responsible for the millisecond fluctuations in the time it takes Earth to rotate once on its own axis. The finding could help to steer spacecraft more accurately.

Researchers have long observed that the spin rate fluctuates with the seasons, in response to shifting wind patterns. Now, a team led by Jean-Louis Le Mouël at the Paris Institute of Geophysics in France has found that this seasonal effect also grows and shrinks in an 11-year cycle, rather like sunspots. Seasons have a bigger effect on spin rate when sunspots are scarce, and a smaller effect when spots are abundant, according to an analysis of data from 1962 to 2009.

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